Polypropylene non-woven fabrics have excellent properties such as breathability and softness and are used as sanitary materials including disposable diapers and sanitary napkins. However, further improvements in their properties have been required. For example, polypropylene non-woven fabrics further improved in softness, bulkiness and mechanical strength are desired.
To obtain non-woven fabrics having excellent softness and bulkiness, various methods have been proposed in which non-woven fabrics are formed of crimped polypropylene fibers. For example, Patent Document 1 discloses non-woven fabrics that comprise conjugated fibers having a crimpable cross-sectional configuration wherein the conjugated fibers comprise a first component comprising propylene polymer and a second component comprising polypropylene with different physical properties from the first component. The second polypropylene is selected from the group consisting of high MFR polypropylenes, low polydispersity polypropylenes, amorphous polypropylenes and elastic (elastomeric) polypropylenes. According to the disclosure, by composite melt spinning the first component and the second component having different physical properties from each other, the resultant conjugated fibers give crimped fibers capable of forming non-woven fabrics with excellent softness and elastic properties.
Patent Document 2 discloses non-woven fabrics that comprise parallel type crimped conjugated fibers comprising ethylene/propylene random copolymer and polypropylene.
Patent Document 3 discloses non-woven fabrics that comprise crimped conjugated fibers comprising two propylene polymers of which a difference between the melting points is 20° C. or more. Patent Document 3 describes that the propylene polymers may be blended with various known additives.
In Patent Document 1, crimped conjugated fibers are obtained from a combination of polypropylenes having dissimilar properties. In detail, Example 1 discloses a combination of polypropylenes having differing MFR and molecular weight distribution in which parallel type conjugated fibers are formed from a first polypropylene having an MFR of 35 and a polydispersity number of 3 and a second polypropylene having an MFR of 25 and a polydispersity number of 2.
The conjugated fibers obtained by combining ethylene/propylene random copolymer and polypropylene that differ in crystallization rate and the crimped conjugated fibers obtained by combining two propylene polymers of which a difference between the melting points is 20° C. or more, as described in Patent Document 2 and Patent Document 3, are excellent in crimp properties. However, depending on applications, non-woven fabrics further excellent in crimp properties and bulkiness are desired.